1. Field of the Invention
The present invention relates to a bidirectional light waveguide telecommunication system for the wavelength separation mode using a passive light waveguide (LWG) bus network.
2. Description of the Prior Art
Recent developments in telecommunication technology have led to integrated services digital networks (ISDN) that have a star or bus structure of light waveguides (LWG) in the level of the subscriber lines. Such communication networks equipped with light waveguides are suitable for narrow-band and broad-band communication, as disclosed in the U.S. No. 3,980,831.
In a light waveguide telecommunication system, the light waveguide extending between two telecommunication locations can be utilized in both transmission directions, in particular upon utilization of, for example, separating routing filters constructed with a partially-reflecting mirror or with an (integrated optical) directional coupler (see Zurich Seminar '86 CONF. Papers, B3, #1 in Table 1), being utilized in the wavelength-isoposition mode or in the wavelength separation mode, i.e. in what is referred to as bidirectional wavelength-division multiplex (WDM) utilizing appropriate wavelength filters (again see Zurich Seminar '86 CONF. Papers, B3, #3 in Table 1), in that the light waves having a shorter wavelength are used for the signal transmission via the optical fibers (preferably monomode) in the one transmission direction and light waves having a longer wavelength are employed for the signal transmission in the opposite transmission direction. In both instances, appropriate optical separating filter modules are to be provided at both ends of the light wave guide, these modules respectively effecting a separate light-guiding connection from the light waveguide to the respective opto-electric transducer and from the respective electro-optical transducer to the light waveguide. Separating routing filters can also be employed in combination with a time separating transmission mode (see Zurich Seminar '86 CONF. Papers, B3, #4.1 in Table 1), whereas, conversely, no additional separating routing filters are to be provided in a time separation transmission mode when the light-emitting diode serving as a transmitter in each of the two telecommunication locations is also used in alternation as a receiving diode that receives the signals coming from the other telecommunication location during the transmission pauses (Japanese Patent 61-89735; Zurich Seminar '86 CONF. Papers, B3, #4.3 in Table 1; German patent 3 822 803; European patent 0 330 190) or, as well, when a monitor photodiode is utilized in alternating fashion as a receiving diode (German patent 3 825 126).
The introduction of new telecommunication systems having LWG central office lines is quite generally dependent on the nature and scope of the pre-existing telecommunication infrastructures having telecommunication services offered therein and on the demand for new broad-band communication services. The potentially greatest market volume is thereby envisioned in the area of private household; this market potential, however, will not take on corporeal form as an effective market demand without correspondingly-low costs of a broad-band subscriber terminal.
It is known, for example, from the European patent 0 171 080 in this context to provide only a single, common light waveguide (LWG) terminal having a respectively shared electrooptical transmission element and opto-electrical reception element for a plurality of (decentralized) subscriber locations in their switching center, whereby a passive LWG bus network provided with optical branchers extends between the common LWG terminal of the switching center and the decentralized subscriber locations. The expense with respect thereto is therefore correspondingly reduced in the switching center, but the expense at the subscriber side is not correspondingly reduced.